The technique of isolated rat liver perfusion developed in our laboratory has been adapted to the use of heterospecies "blood" consisting of a suspension of bovine red cells in Krebs-Ringer bicarbonate buffer containing 3 percent of defatted bovine serum albumin. Thus, with this perfusion medium, initial perfusate levels of rat plasma proteins are very low and permit accurate, specific serological measurement of net increases in rat serum albumin, fibrinogen, alpha 1-acid glycoprotein, alpha 2-(acute phase) globulin and haptoglobin, during experiments routinely 12 hrs in duration -- 24 hrs in special cases. Experiments to be conducted in vivo and especially in the isolated perfused rat liver system will continue, and extend our study of factors regulating net synthesis of the above plasma proteins to include transferrin, alpha 2-U-globulin (the male sex protein), hemopexin and ceruloplasmin. Factors to be further investigated include those in the liver donors; namely, experimental tissue injury (e.g. sterile turpentine abscess), protracted fasting, endocrine ablations and iron deficiency. Factors to be evaluated directly in the course of perfusion will include continuous infusion of amino acids plus glucose (basal condition) plus hormones including insulin, cortisol, growth hormone, glucagon, triiodothyronine, ACTH, epinephrine, and acetylcholine. Effects of variation in perfusate pH and liver temperature deserve additional study. Our indirect evaluation of the half-lives of mRNA's of specific plasma proteins in terms of altered rates of synthesis of specific proteins is to be extended to include all of the above mentioned proteins. The preparation of specific solid immunoabsorbents for the isolation of sfpecific plasma protein-polysome complexes is being tested for albumin; if successful, it will be applied to alpha 1-acid glycoprotein.